Question 433 of 2,152
NetFlow and Flexible NetFlowhardMultiple ChoiceObjective-mapped

Quick Answer

The answer is a misconfigured flow monitor applied to the BGP peering interface in the input direction, using a match ip address prefix-list that denies the prefix 10.1.1.0/24, which prevents the route reflector from processing and reflecting the route. This occurs because Flexible NetFlow, when applied to an interface, can intercept incoming BGP updates before they reach the BGP process; if the flow monitor’s match statement filters the prefix, the router never installs or advertises it to clients, even though the BGP session remains up and the route exists in the table. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how control-plane traffic interacts with data-plane monitoring features—a common trap is assuming BGP filtering only happens via route-maps or prefix-lists, overlooking that a flow monitor’s match clause can silently drop updates. Remember the memory tip: “Flow before BGP—if the monitor denies it, the reflector never sees it.”

300-410 NetFlow and Flexible NetFlow Practice Question

This 300-410 practice question tests your understanding of netflow and flexible netflow. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A BGP-based network uses route reflectors and Flexible NetFlow to monitor traffic. After applying a flow monitor to the route reflector's interface, some BGP routes are not being reflected to clients. Router R1 (route reflector) shows: show bgp vpnv4 unicast all neighbors 10.0.0.2 advertised-routes | include (10.1.1.0/24) No entries. The BGP session is up, and the route 10.1.1.0/24 is in the BGP table. What is the root cause?

Question 1hardmultiple choice
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Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

The flow monitor is applied to the BGP peering interface in the input direction, and it uses a match ip address prefix-list that denies the prefix 10.1.1.0/24, causing the route reflector to not process the route.

Flexible NetFlow can be configured with a flow record that includes BGP attributes, but if the flow monitor is applied to the interface used for BGP peering, it might cause the router to process BGP updates differently. Specifically, if the flow monitor is configured to use a flow record that includes the 'bgp next-hop' or 'bgp community' fields, it might require the router to perform additional processing, which could delay or prevent the reflection of routes. However, the most likely root cause is that the flow monitor is configured with a match statement that matches on BGP communities, and the route 10.1.1.0/24 has a community that is being filtered by the flow monitor's match statement, causing the route to be dropped from the advertised routes. But since the flow monitor does not filter routes, the correct answer is that the flow exporter is misconfigured to use the BGP next-hop as the source, causing the route reflector to change the next-hop to itself, but the flow monitor's configuration interferes with the next-hop processing. Actually, the correct answer is that the flow monitor is using a flow record that includes the 'ipv4 next-hop' field, and the route reflector is configured to not change the next-hop, but the flow monitor's processing causes the next-hop to be overwritten, making the route invalid for clients.

Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • The flow monitor is configured with a flow record that includes the 'bgp next-hop' field, causing the route reflector to change the next-hop to itself, which is not reachable by clients.

    Why it's wrong here

    Flexible NetFlow does not modify BGP attributes; it only monitors them.

  • The flow exporter is configured to use the BGP neighbor's IP as the destination, but the exporter is not reachable, causing BGP updates to be delayed.

    Why it's wrong here

    The exporter destination is for NetFlow data, not BGP updates.

  • The flow monitor is applied to the BGP peering interface in the input direction, and it uses a match ip address prefix-list that denies the prefix 10.1.1.0/24, causing the route reflector to not process the route.

    Why this is correct

    If the flow monitor uses a match ip address prefix-list to filter flows, and that prefix-list denies the route's prefix, the router may not process the BGP update correctly, leading to the route not being reflected.

    Related concept

    OSPF neighbours must agree on key parameters.

  • The BGP route reflector is configured with a cluster ID that conflicts with the flow monitor's settings.

    Why it's wrong here

    Cluster ID is unrelated to NetFlow.

Common exam traps

Common exam trap: OSPF can fail even when IP connectivity looks correct

OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.

Detailed technical explanation

How to think about this question

OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.

KKey Concepts to Remember

  • OSPF neighbours must agree on key parameters.
  • Router ID selection can affect neighbour relationships and LSDB output.
  • OSPF cost influences the preferred path.
  • A route can appear in OSPF information but not become the installed route.

TExam Day Tips

  • Check area mismatch first when OSPF adjacency fails.
  • Review passive interfaces when a network is advertised but no neighbour forms.
  • Use show ip ospf neighbor and show ip route clues carefully.

Key takeaway

OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

Real-world example

How this comes up in practice

A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.

What to study next

Got this wrong? Here's your next step.

Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.

Related practice questions

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FAQ

Questions learners often ask

What does this 300-410 question test?

NetFlow and Flexible NetFlow — This question tests NetFlow and Flexible NetFlow — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: The flow monitor is applied to the BGP peering interface in the input direction, and it uses a match ip address prefix-list that denies the prefix 10.1.1.0/24, causing the route reflector to not process the route. — Flexible NetFlow can be configured with a flow record that includes BGP attributes, but if the flow monitor is applied to the interface used for BGP peering, it might cause the router to process BGP updates differently. Specifically, if the flow monitor is configured to use a flow record that includes the 'bgp next-hop' or 'bgp community' fields, it might require the router to perform additional processing, which could delay or prevent the reflection of routes. However, the most likely root cause is that the flow monitor is configured with a match statement that matches on BGP communities, and the route 10.1.1.0/24 has a community that is being filtered by the flow monitor's match statement, causing the route to be dropped from the advertised routes. But since the flow monitor does not filter routes, the correct answer is that the flow exporter is misconfigured to use the BGP next-hop as the source, causing the route reflector to change the next-hop to itself, but the flow monitor's configuration interferes with the next-hop processing. Actually, the correct answer is that the flow monitor is using a flow record that includes the 'ipv4 next-hop' field, and the route reflector is configured to not change the next-hop, but the flow monitor's processing causes the next-hop to be overwritten, making the route invalid for clients.

What should I do if I get this 300-410 question wrong?

Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.

What is the key concept behind this question?

OSPF neighbours must agree on key parameters.

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Last reviewed: Jun 19, 2026

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